Lecture 11: Parasitism

What are characteristics of a parasite?

• lives in or on another organism (host)

• consumes host resources or some tissues

• some use the host to infect another host or to reach other habitats

• different degree of host specificity

• lots of parasites are nonpathogenic (harmless)

What is an infection?

invasion of body tissues by other organisms

What is a pathogen?

parasite that causes an infectious disease (symptoms). Harms host

T/F all parasites are pathogenic

False, not all are pathogenic

T/F Parasites are always a bad thing

false, not always a bad thing

What are the modes of transmitting parasites?

• exchange of body fluids or tissues

• vectors

• skin penetration

• ingestion

• breathing in spores and general airborne

• physical contact

What are vectors?

an insect or animal that transmit disease to other animals or humans

What is an example of a vector?

mosquitos

What are ectoparasites?

Mostly arthopods (ticks, mites, lice, fleas, etc.), some leeches, lampreys, some nematodes on plants

Nematodes can be ectoparasites for who?

for plants, not humans

Most ectoparasites do what?

suck the blood and then leave

What types of endoparasites are there?

intracellular and intercellular

What are intracellular endoparasites?

live inside the cells of a host

What are intercellular endoparasites?

live in spaces between cells of a host

What are examples of endoparasites?

• viruses

• prions

• protozoans

• bacteria

• fungi

• helminths

What are prions?

they begin as beneficial brain protein. It folds into an incorrect shape and becomes pathogenic

How do prions replicate?

by coming into contact with other proteins

What are examples of prions?

• bovine spongiform encephalopathy (mad cow disease)

• chronic wasting disease in deer, elk, and moose

Are prions living organisms?

No

How do some researchers feel about prions?

some say they are not parasites since they are not living organisms

What are viruses?

Composed of genome of nucleic acid surrounded by a protein coat called a capsid

How do viruses reproduce?

within cells using the cells metabolic pathways

What examples of viruses?

• HIV: AIDS

• H5N1 (“bird flu”): jumps to humans

• west nile virus

• COVID-19

How is the west nile virus transmitted? and who does it affect?

• by mosquitos

• affects birds and humans

Where was HIV initially found?

in chimps

Do parasites intend to kill hosts? Why or why not?

They do not because it is not beneficial for them to lose their host

What are bacteria?

single-celled prokaryotes

Do bacteria have a nucleus?

No

What are examples of bacterial infections?

• anthrax

• plague

• pneumonia

• salmonella

• leprosy

What are protozoans?

unicellular eucaryotes, some colonial

What are examples of protozoans?

• trypanosoma

• giardia

Prokaryotes vs. eukaryotes

eukaryotes have a nucleus and organelles and prokaryotes do not

What are fungi?

eukaryotic unicellular and multicellular organisms

What are examples of fungi?

• chytridiomycosis

• white-nosed bat syndrome

What are helminths?

“worms”: platyhelminthes, nematoda and acanthocephala

Which are the most diverse helminths?

flatworms and roundworms

Do we need a microscope to see helminths?

generally no

What are the main types of hosts in the helminths life cycle?

intermediate host and definitive (final) host

What is an intermediate host?

a host needed in the course of the parasite’s life cycle in which there is development to a next larval stage. The parasite may multiply asexually

what is a Definitive (final) host?

host in which the parasite sexually matures and exhibits sexual reproduction

T/F parasites need multiple hosts in their lifetime

true

Explain the complex life cycle of endoparasites known as clonorchis sinensis

the host of this parasite needs to be a snail at some point, if not they die. Therefore, they need to have the ability to recognize hosts

What are the mechanisms of parasite transmission?

Horizontal transmission and vertical transmission

What is horizontal transmission?

when a parasite moves between individuals other than parents and their offspring

What is an example of horizontal transmission?

a mosquito biting a bird and transmitting parasites to it

What is vertical transmission?

when a parasite is transmitted from a parent to its offspring

What is an example of vertical transmission?

• a mother nesting w/ her chicks and the mother passes parasites to chicks

• or mother is pregnant, passes parasites to offspring bc it crosses the placenta

Anything coming from mom or dad=

vertical transmission

anything coming from anything other than mom or dad=

horizontal transmission

What are factors that influence parasite-host dynamics?

• mode of entering the host

• population density (higher = closer contact)

• host’s immune system

• ability of parasite to jump between species

• existence of reservoir specices

• in human populations: hygiene and modern traveling can be important

• implant: monocultures

Explain this model. and what does R0 mean?

• model on dynamics of a nonlethal infection over time

• the disease spreads whenever the number of newly infected individuals is greater than the number of recovered individuals

• R0= reproductive ratio: number of secondary cases produced by primary cases

Explain parasite adaptation in snails.

• infected by platyhelminthes

• host acts differently because it is under the influence of the parasite

• snails begin to move upward

• eyestalks are enlarged and banded

• in effect are easily noticed by birds

Explain parasite adaptation in yellow dungflys.

• yellow dungfly is infected by fungus

• the fungus causes the fly to perch upside-down on an upper leaf of a plant

• spores are released, wind infects more flies

Explain these graphs.

• forest tent caterpillars have population densities that cycle every 10-15 yrs

• viruses increase abundance shortly after caterpillar densities increases

• many caterpillars die

• high density= more transmission= mortality= prevalence of the disease declines

What is coevolution in host-parasite interactions?

two ore more species evolve in response to each other’s evolution

Explain this graph.

• Decline of rabbit mortality over time. More resistant host population and less lethal pathogen

• measures immune responses

Explain the invasive rabbits in Australia situation

• Rabbits were not native to Australia and were brought over

• too many reproduced and were becoming uncontrolable

• they introduced a virus (Myxoma) to attempt to take them out

• mortality rate was huge

• rabbits that survived reproduced and passed on resistance

• pathogen became less effective